A problem was required to be eliminated in which when designating a keyword as a search condition (hereinafter, search condition character string) and searching the full text, a text containing only a keyword similar to the search condition character string is erroneously searched. For example, if  (Kyoto) is designated as a search condition character string for searching, a text such as  (Tokyo-to de jissi sareteiru) may have been searched (since  (Tokyo-to) and  (Kyoto) are different from each other,  (Tokyo-to de jissi sareteiru) should not have been searched).
Conventionally, the morphological analysis method and the Ngram method are widely known as a text search technique but each method has the following disadvantages. In the morphological analysis method,  (Tokyo-to) is not a hit even when searching is carried out by  (Kyoto). In the morphological analysis method, however, a search dictionary needs to be previously defined and uncommon and strange search words and phrases are not contained in the dictionary definitions for searching for new words/phrases and minor words/phrases, and consequently perfect definition is impossible even when redefining is frequently performed, and a large load is imposed on the definition work.
On the contrary, in the Ngram method in which an input text is “delimited by character strings of N characters”, the words contained in the text are ignored and the text is recognized as words in units of N characters so that a dictionary as in the morphological analysis method is not required. However, a text containing  (Tokyo-to) is output when searching is carried out by  (Kyoto), while even a text containing both  (Kyoto) and  (Tokyo-to) (such as a text of  (Kyoto to Tokyo-to de jissi sareteiru)) is not output when the searching with  (Tokyo-to) designated as exclusion condition (the searching when a search condition character string is contained in an exclusion condition character string) is conducted.
As a supplement for the disadvantage of the Ngram method, a position in which a hit keyword is present (address) is held and character strings before and after the hit keyword are extracted to confirm whether the extracted character strings are an exclusion condition character string so that a text containing the search condition character string (such as a text of  (Kyoto to Tokyo-to de jissi sareteiru)) can be searched even when  (Kyoto) is designated as the search condition character string and  (Tokyo-to) is designated as the exclusion condition character string (see Japanese Laid-open Patent Publication No. 2003-203093, for example).
Since the amount of memory consumption for holding an address increases and a confirmation needs to be made as to whether a character string is an exclusion condition character string even when a conventional search method for compensating for the disadvantages of the Ngram method is used, there is a problem that a search processing can not be performed rapidly.